Japanese Patent Laying-open No. 2004-120844 discloses a control device for a boost converter used in combination with an inverter. This control device operates in response to a difference between a detected output voltage value and an output voltage control value to control a duty ratio of a converter switching device by feedback by proportional-plus-integral control.
The control device obtains the inverter's output power value by an operation circuit and compares the value with a predetermined value by a comparator to determine a path of a current of the converter and in accordance with a result of the determination outputs from a correction circuit an amount of correcting the duty ratio to minimize or prevent variation of the voltage of the converter.
In recent years, electric automobiles, hybrid automobiles, fuel cell automobiles and other similar automobiles that adopt an alternate current motor as a driving source for propelling the vehicle and mount therein an inverter device driving the alternate current motor, have made their appearances.
Some such vehicles mount therein batteries of two or more different voltages, such as a high voltage battery for driving a motor for propelling the vehicle and a low voltage battery for auxiliary machines.
Furthermore, when an automobile having a fuel cell mounted therein starts operation, the fuel cell outputs a voltage, which varies before a steady output is attained. Accordingly, combining the fuel cell with a secondary battery and connecting them together by a voltage converter for use is being studied to ensure steady driving power.
The fuel cell's output voltage and the secondary battery's output voltage both vary with the vehicle's state. Accordingly, the voltage converter connected therebetween operates to supply a current from the secondary battery to the fuel cell and vice versa in accordance with the power required for the vehicle.
Accordingly there is a demand for a voltage converter that can quickly output required voltage in accordance with the vehicle's acceleration, the road's inclination and the like.
Furthermore Japanese Patent Laying-open No. 2004-120844 discloses determining an amount of correcting a duty ratio in accordance with the power output from the inverter. For a system having a fuel cell connected adjacent to an inverter, however, the inverter's output voltage alone can be insufficient for obtaining a correct, optimum amount of correction.